1. Technical Field
The present disclosure relates to an exposing process for manufacturing semiconductor devices; more particularly, a method of exposing a wafer to a light, thereby transferring a pattern on a reticle onto the wafer, and an apparatus for performing the exposing method that includes a reticle assembly.
2. Discussion of Related Art
Generally, semiconductor devices are manufactured by performing a fabrication (FAB) process for forming an electric circuit on a semiconductor substrate, an electrical die sorting (EDS) process for inspecting electrical characteristics of the electric circuit, and a packaging process for separating the semiconductor substrate into individual semiconductor chips and sealing each of the semiconductor chips using, for example, an epoxy resin.
The FAB process includes a deposition process for forming a thin layer on the semiconductor substrate, a chemical mechanical polishing (CMP) process for polishing the thin layer, a photolithography process for forming a photoresist pattern on the thin layer, an etching process for etching the thin layer into an electrical pattern using the photoresist pattern as a mask, an ion implantation process for implanting ions into a region of the semiconductor substrate, a cleaning process for cleaning impurities from the semiconductor substrate, and an inspection process for inspecting a surface of the semiconductor substrate to detect defects in the thin layer or in the electrical pattern.
The photolithography process includes a coating process for coating a photoresist composition layer on a silicon wafer, a baking process for hardening the photoresist composition layer into a photoresist film, an exposing process for transferring a pattern on the reticle (i.e., a reticle pattern) onto the photoresist film, and a developing process for forming the photoresist pattern along the transferred reticle pattern.
An exposure apparatus for performing the exposing process includes a light source, an illumination unit for illuminating the reticle with a light from the light source, a reticle stage for supporting the reticle, a projection optical system for projecting a light passing through the reticle onto the wafer, and a wafer stage for supporting the wafer. Examples of the exposure apparatus are disclosed in U.S. Pat. No. 6,331,885 (issued to Nishi) and U.S. Pat. No. 6,538,719 (issued to Takahashi et al.).
The reticle has a pattern corresponding to an image transferred onto a plurality of shot areas defined on the wafer. The reticle stage is disposed over the projection optical system. The wafer stage is disposed under the projection optical system.
An illumination light is generated from the light source. The reticle is irradiated by the illumination light having passed through the illumination unit during the exposing process. The reticle stage moves horizontally for transforming the illumination light passing through the reticle into a projection light. The projection light contains image information after passing through the reticle. The wafer stage moves in an opposite direction to the reticle stage so that the projection light transfers the image information onto the wafer.
A quantity and a size of the shot areas may be determined in accordance with a characteristic and a usage of the semiconductor device. The exposing process includes a first exposing process performed on the shot areas and a second exposing process performed on edge shot areas. The edge shot areas are adjacent to edge portions of the wafer. The first exposing process may be performed on all the shot areas of the wafer. Alternatively, the first exposing process may be performed on all the shot areas except for the edge shot areas of the wafer. The second exposing process removes the photoresist film on die areas adjacent to the edge portion of the wafer.
In a conventional single exposing process, the first exposing process may use a conventional reticle having a single pattern as an exposure mask. The second exposing process in the conventional single exposing process may use a non-patterned reticle as the exposure mask. In a conventional multiple exposing process, a reticle having a multiple pattern areas may be used as the exposure mask.
In the conventional single exposing process, for performing the second exposing process, the conventional reticle needs to be replaced with the non-patterned reticle after completing the first exposing process. In the conventional multiple exposing process, the number of the shot areas may increase because the pattern area of the reticle in the first exposing process is smaller than that of the conventional reticle.
A need, therefore, exists to improve an exposure method and an exposure apparatus to reduce time loss in the conventional single exposing process and the conventional multiple exposing process.